Apparatus as briefly defined in the foregoing, may be utilized in the mining of ores or the like and they may be employed in excavating mining of coal.
The excavating head of an excavating boom may comprise a conical tool carrying cutting blades which, on rotation of the tool will perform a cutting or milling action on and into the material that is to be worked on, i.e. the face of the tunnel. In order to increase their longevity, the cutting or milling blades, picks or teeth are customarily equipped with wear resistant hardfacing metal cutting edges.
In known apparatus of this type, the opening that is obtained in the mine face is obtained by milling away material, step-wise, to enlarge an initially obtained opening. Thus, once such an opening has been formed, either by the same machine or by blasting a suitable hole into the material to be worked on, the opening is then enlarged to the desired size, e.g., when a tunneling operation is performed, until the desired cross-section of the tunnel has been reached; or, when mining is carried out, until the full cross-section of the ore body or vein has been excavated. Thus, the material is removed by a milling action. Such an operation is difficult and results in considerable wear of the cutting tools.
With such apparatus, the excavating boom is displaced such that it must gradually eat away the entire cross-section of the area worked on. This means that the machine will then reach its operating limits where the neighboring material is harder, e.g., the transition from coal to bedrock, or, in other words, the wear of the equipment will then become prohibitive for economical operation. Furthermore, the efficiency of the apparatus is lower then harder material is worked on by the apparatus. Then, as well, the progress of the apparatus in the excavation is retarded.
Apparatus has been proposed, generally for use in other fields and of different structure for service for other purposes. In these a support is equipped with heavy duty hydraulic hammers which are capable of producing a high impact. The hammers are, usually, attached by means of booms to scoop excavators. These hammers initially work into the relatively soft coal seam in order to break it up and then work on the stone head wall. Such machinery is considered obsolete for present day requirements in tunneling operations.
I have previously described (U.S. Pat. No. 3,729,056), on a caterpillar of like fulltrack support member, a boom or outrigger which may be rotated by means of a motor as required about a horizontal axis and provided with a milling cutter. This apparatus is further equipped with a conveying means for the transporting of the recovered material.
An additional articulated boom is arranged movably with respect to the support member and has a hydraulically actuated hammer mounted thereon.
In this arrangement the hammer is attached to a base or carriage on the excavating miller boom via a relatively articulated boom and the base may be moved in the longitudinal direction with respect to the apparatus. The hammer is employed when a harder portion or area is to be worked on in an alternating fashion which requires that the milling boom or the hammer boom is actuated, i.e. extended or retracted, in order to bring the hammer into an effective working position with respect to the material to be worked on.
This is, of course, time consuming and thus not too efficient at times. Simultaneous operation of the hammer and the excavating head on the excavating boom at different points of attack cannot be carried out. Thus it is not possible to utilize the excavating head in a lowermost operating position when the hammer has to perform, simultaneously, at a lower power requirement in a head wall area. When the hammer is used, the milling tool is usually tilted excessively and cannot operate effectively.
In summary, the devices according to the prior art do not work with the same efficiency across the entire cross-section of the area to be worked on. That is, in a lower working position or at an upper working position, with respect to the horizontal, the maximum extension of the excavating boom will result in such angles or inclinations of the equipment that do not lend themselves to the most efficient operation of the apparatus.
Of course, devices have been proposed in the past which would mill or excavate at one time the entire cross-sectional area to be obtained while simultaneously also advancing. These are variously equipped with milling tools, rotating chisels or the like. Such machinery has to be brought into direct contact with the material to be worked on under relative high pressure which in turn requires that the devices are properly supported. This becomes time consuming and next to impossible where no suitable counterpressure surfaces are available, i.e. the walls are too soft.